The present invention relates to reduced nitrogen oxide (NOx) emission fuel compositions, more particularly, to high stability fuel compositions for use in internal combustion engines.
Nitrogen oxides comprise a major irritant in smog and are believed to contribute to tropospheric ozone which is a known threat to health. Environmental considerations and government regulations have increased the need to reduce NOx production. One problem with using diesel-fueled engines is that the relatively high flame temperatures reached during combustion increase the tendency for the production of nitrogen oxides (NOx). These are formed from both the combination of nitrogen and oxygen in the combustion chamber and from the oxidation of organic nitrogen species in the fuel. Various methods for reducing NOx production include the use of catalytic converters, engine timing changes, exhaust recirculation, and the burning of “clean” fuels. These methods are generally too expensive and/or too complicated to be placed in widespread use. The rates at which NOx are formed is related to the flame temperature. It has been shown that a small reduction in flame temperature can result in a large reduction in the production of nitrogen oxides.
One approach to lowering the flame temperature is to inject water in the combustion zone, however; this requires costly and complicated changes in engine design. An alternate method of using water to reduce flame temperature is the use of aqueous fuels incorporating both water and fuel into an emulsion. Gravitational phase separation (during storage) and high temperature high pressure/shear flow rate phase separation (in a working engine) of these emulsions present the major hurdle preventing their commercial use.
Additional problems that may occur from long-term use of aqueous fuels include engine corrosion, engine wear, or precipitate deposition which may lead to engine problems and ultimately to engine inoperability. Problematic precipitate depositions include coalescing ionic species resulting in filter plugging and inorganic post combustion deposits resulting in turbo fouling. Another problem related to aqueous fuel compositions is that they often require substantial engine modifications, such as the addition of in-line homogenizers, thereby limiting their commercial utility.
The present invention addresses the problems associated with the use of aqueous fuel compositions by providing a stabile, inexpensive fuel emulsion with reduced NOx and particulate emissions.